Inductive tuner



A Ag. v13, 1946. w. H. KUNz -INDUCTIVE TUNER Filed May 5, 1944 IN V EN TOR. Walden ZZ 21112 i from/Er Patented Aug. 13, 1946 ENDUCTIVE TUNER Walden H. Kunz, Jackson, Mich., assignor to P. R.

Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Application May 5, 1944, Serial No. 534,216

(Cl. YY1-242) 2 Claims. l

This invention relates to continuously variable inductive tuning devices and has for its object to provide a device of this type having novel and improved details of construction and features of opera-tion.

Another object of the invention is to provide an inductive tuner of the above type having a new and improved rotary contact member and associated control elements which are particularly adapted for use with inductance coils of small diameter.

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

Slide-wire variable inductance devices are used for tuning radio receivers, oscillators and various other electric and electronic instruments and devices. Generally, they comprise a bare wire coil wound on a suitable insulating form which is mounted on a shaft so as to rotate about its axis, and a sliding Contact tracking on a stationary trolley rod slides along the wire of the coil in electrical contact therewith as the coil is rotated. The mechanical and electrical requirements of such inductive tuning devices are severe, especially since positive and constant contact must be maintained for electrical reasons, while at the same time lightness of contact is required for ease of tuning and to keep down wear over long periods of use.

The present invention provides a tuning device of the foregoing type in which the Wire coil is stationary and in which tuning is effected by rotating the sliding contact member over the convolutions of the coil, The Contact itself comprises a si r-le piece of light spring material having contacting nibs at its ends engaging the coil and a central Contact portion in sliding engagement with an axially extending trolley rod which is adapted to be rotated around the coil. As the troley rod is rotated about the coil, as by means of a shaft extending axially through the coil, the spring contact slides along the convolutions of the wire and at the same time slides longitudinally on the trolley rod, insuring a positive and constant contact with a minimum of friction and wear.

Another feature of the invention resides in the provision of a novel stop mechanism for arresting the movement of the spring contact at either end of its travel without exerting any pressure on the Contact itself, thus eliminating any possibility of bending or otherwise damaging the contact or the associated electrical connections.

Although the novel features which are characteristic of the invention are set forth more in detail in the claims appended hereto, the nature and scope of the invention may be better understood by referring to the following description, taken in connection with the accompanying drawing forming a part thereof, in which a specic embodiment has been set forth for purposes of illustration.

In the drawing:

Fig. l is a side elevation of a continuously variable inductive tuning device embodying the invention;

Fig. 2 is a longitudinal section taken on the line 2--2 of Fig. l;

Fig. 3 is a transverse section taken on the line 3-3 of Fig. 2; and

Fig. 4 is a transverse section taken on line i-fl of Fig. 2.

In the following description certain specific terms are used for convenience in referring to the various details of the invention. These terms, however, are to be interpreted in accordance with the state of the art.

The variable inductive tuning device shown in A the drawing comprises a support or end plate Iii carrying a coil form II of insulating material such as resin impregnated ber. The form is shown as cylindrical but it is understood that it may be made conical or frusto-conical if desired.

A bare wire coil I2 is wound on the surface of form II with adjacent turns spaced from each other. If desired, the form may be provided with a shallow groove in which the wire I2 is wound. rihe coil may suitably be made of hard drawn copper wire plated with silver, and, if desired, coated with a protective lubricant.

One end I3 of the coil I2 is soldered to a terminal I4 mounted on an insulating block l5 which is secured to the end plate I0 by stud iii. The opposite end of the coil is soldered to a metal disc I'I fixed to the outer end of the coil form I i. The disc I'I carries a bearing sleeve I8 within the bore I9 of the form II which is connected by a wire 2B to a second terminal similar to the terminal I4. The wire 2) extends through the bore I9 and radially through the form II at a point adjacent the second terminal.

A second bearing sleeve 2| is positioned within the end of the bore I9 opposite the sleeve I8 and a rotatable control shaft 22 of insulating material extends axially through both sleeves and through the coil form II, one end of said shaft projecting outwardly beyond end Plate Ill to receive a suitable control knob, while the opposite end of the shaft extends outwardly of the coil form past the end disc Il.

A hub 23 is secured to the inner end of the shaft 22 by set screw 24; and an arm 25 secured to hub 23 carries a trolley rod 26 which extends axially along the side of coil form Il parallel to the cylindrical surface thereof. The arm 25 and trolley rod 25 are composed of suitable conducting material, and between them is secured a forkshaped contact spring 2l' having silver alloy contact brushes 28 which slide on the metal disc Il on the inner end of coil form Il, thereby providing a slip ring connection to the end of the coil and to the contact to be desired.

A stop member 29 is slidably mounted on trolley rod 26. The stop member 23 is formed of Bakelite, ceramic or other suitable insulating material and, in the embodiment illustrated, is of generally tubularl shape with a substantially semi-circular opening intermediate its ends exposing the trolley rod 2t through said opening.

A sliding contact member 3D, preferably stamped in a single piece from sheet spring metal, has its central portion bent to form a semi-circular channel 3l which fits within the opening of stop member 29 and engages the trolley rod 25, while the outer ends of the contact member are formed to provide narrow channel-shaped nibs 32 conforming to and engaging the wire of coil l2. The nibs 32 rest on the same turn of coil I 2 at spaced points thereon and one nib is slightly twisted or skewed with respect to the other to allow for the pitch angle of the helical coil.

It will be evident that as the shaft 22 is rotated, causing trolley rod 26 to rotate about'the cylindrical surface of coil form ll, the nibs 32 of contact member 30 slide along the wire i2 and move the member 3S and stop member 29 lengthwise along the trolley rod. The contact member 30 is connected by the trolley rod 26, contact spring 2l', contacts 28, disc il and Wire 20 to the terminal I4.

In accordance with a feature of the invention, I provide stop members or lugs 34 and 35 on the cylindrical surface of coil form Il, adjacent opposite ends thereof, for engagement with the slidable stop member 29 whenever the trolley rod 25 is rotated suiciently to bring the contact member 3l) near either end of the coil l2. The lugs 34 and 35 are so positioned that, when the contact member 30 reaches a point adjacent the end of the coil, the leading side of stop member 29 will strike against the side of lug 34 or 35, as the case may be, and thus prevent further rotation of the trolley rod.

A particular advantage of the foregoing construction is that the impact of stop member 29 against lugs 34 and 35 is completely isolated from the delicate spring contact member 30 and therefore cannot injure said contact member, noi can the nibs 32 of the contact member over-run the ends of the coil or strike against the soldered ends thereof. The contact member 353 is originally bent just enough to provide the proper spring pressure on the nibs when the member is interposed between the rod 26 and the coil, and my improved construction enables this initial adjustment to be maintained indefinitely under all conditions of use.

While the present invention has been described herein as carried out in a specific embodiment, it is not to be limited thereto, but is only to be restricted in accordance with the spirit and scope of the appended claims.

What is claimed is:

1. A Variable. inductance device comprising in combination a coil form of circular cross section. a bare helical conductive coil wound thereon, a rotatable shaft extending axially through said coil form, a trolley rod carried by said shaft adjacent and parallel to said coil form and mounted to be rotated about said coil by said shaft, a contact element integrally formed of a single piece of sheet metal in a substantially symmetrical and dynamically balanced shape, the ends of said element being bent into smooth-surfaced grooved contact nibs engaging the wire of said coil in the grooves therein and the mid-portion of said element being bent into a smooth-surfaced transverse channel which is concave on the opposite :face of said element from said grooves and engages the trolley rod, said contact element being biased to produce smoothly sliding and uniformly distributed spring pressure against said coil at said nibs and against said rod at said channel for movement along said rod when said shaft is rotated, a disc mounted on the inner end of said coil form, a spring contact arm attached to said trolley rod having sliding contact means with said disc, and a terminal connected to said disc.

2; A variable inductance device comprising in combination a coil form of circular cross section, a bare helical conductive coil wound thereon, an axially disposed bearing sleeve at each end of said coil form, a shaft extending axially through said coil form and rotatable in said bearing sleeves, a trolley rod carried by said shaft adjacent and parallel to said coil formv and mounted to be rotated about said coil by said shaft, a contact element integrally formed of a single piece of sheet metal in a substantially symmetrical and dynamically balanced shape, the ends of said element being bent into smooth-surfaced grooved contact nibs engaging the wire of said coil in the grooves therein and the mid-portion of said element being bent into a smooth-surfaced transverse channel which is concave on the opposite face of said element from said grooves and engages the trolley rod, said contact element being biased to produce smoothly sliding and uniformly distributed spring pressure against said coils at said nibs and against said rod at said channel for movement along said rod when said shaft is rotated, a disc integrally formed with the bearing sleeve at the inner end of said coil form, a spring contact arm attached to said trolley rod having sliding contact means with said disc, and a terminal connected to said sleeve.

WALDEN H. KUNZ. 

